The invention relates to a mobile radio receiver for cellular radio telecommunications systems according to the precharacterizing clause of patent claim 1.
Two of the currently most powerful wire-free telecommunications systems are the mobile radio system based on the GSM Standard (Global System for Mobile Communication; see Informatik Spektrum [Information Spectrum] 14 (June 1991), No. 3, Berlin; A. Mann: xe2x80x9cDer GSM-Standardxe2x80x94Grundlage fxc3xcr digitale europxc3xa4ische Mobil-funknetzexe2x80x9d [The GSM Standardxe2x80x94Basis of European digital mobile radio networks]; pages 137 to 152) and the cordless telephone system based on the DECT Standard (Digital Enhanced (previously: European) Cordless Telecommunications; cf. (1): Nachrichtentechnik Elektronik [Electronic Information Technology] 42 (January/February 1992), No. 1, Berlin; U. Pilger: xe2x80x9cStruktur des DECT-Standardsxe2x80x9d [Structure of the DECT Standard]; pages 23 to 29 in conjunction with the ETSI Publication ETS 300175-1 . . . 9, October 1992; (2): Siemens Components 31 (1993), No. 6; S. Althammer and D. Brxc3xcckmann: xe2x80x9cHochoptimierte IC""s fxc3xcr DECT-Schnurlostelefone [Highly optimized ICs for DECT cordless telephones]xe2x80x9d, pages 215 to 218; (3): telecom report 16 (1993), No. 1, J. H. Koch: xe2x80x9cDigitaler Komfort fxc3xcr schnurlose Telekommunikation xe2x80x94DECT-Standard erxc3x6ffnet neue Nutzungsgebiete [Digital convenience for cordless telecommunicationsxe2x80x94DECT Standard opens up new fields of use]xe2x80x9d, pages 26 and 27), both of which transmit radio messages inter alia using the TDMA method (Time Division Multiple Access).
However, the present invention is not limited either to these two telecommunications systems or to the TDMA transmission method. The invention thus also extends to those systems which are described in the document TIB-R09067 (5)-P. Bauer-Trocheris: xe2x80x9cUMTS-Integrator fxc3xcr die mobile Kommunikationxe2x80x94ein Ausblick auf die Mobilfunklandschaft nach dem Jahr 2000 [UMTS integrator for mobile communicationsxe2x80x94a summary of the mobile radio situation after the year 2000]xe2x80x9d, Report on the Convention xe2x80x9cEuropean Mobile Radio, 5th annual meeting of German and European mobile radio industry, FIBA Congresses, Munich, Feb. 24 to 26 1993xe2x80x9d.
The GSM mobile radio system is a digital cellular system in which, according to FIG. 1 (see tec February 1993xe2x80x94The technical magazine Ascom xe2x80x9cWege zur universellen mobilen Telekommunikationxe2x80x9d [Ways for universal mobile telecommunication], pages 35 to 42) a large number of base stations BST1 . . . BST3 are split into cells in a cellular supply region. The cells and the base stations BST1 . . . BST3 are connected to one another and to the outside world via a mobile switching center MSC1, MSC2 (Mobile Switching Center). For an efficient network design, usually a number of these mobile switching centers MSC are combined in a public state-based mobile network PLMN1, PLMN2 (Public Land Mobile Network). Furthermore, the mobile switching centers MSC1, MSC2 are linked to a public telephone network PSTN (Public Switched Telephone Network). A mobile radio part MFT1 . . . MFT3, from which a call is normally passed, is, as a rule, operated by that base station with which the best radio link can be maintained. In GSM mobile radio, the users under some circumstances move at high speed in the cellular supply region. This leads to a number of mobile radio cells being traversed during a call. In order to ensure an interruption-free handover from one adjacent cell to another adjacent cell (seamless handover), special protocols are required between the mobile radio part and the base station.
The DECT-specific cordless telephone system is a digital system which, according to FIG. 1 (cf. tec February 1993xe2x80x94Technical Magazine from Ascom xe2x80x9cWege zur universellen mobilen Telekommunikation [Ways for universal mobile telephone communication]xe2x80x9d, pages 35 to 42) can be used in the private area (for example house, apartment, garden etc.), in the small public area (for example companies, office building etc.) and as a telepoint application.
The basic structure of the cordless telephone system comprises a base station BS (FP=Fixed Part with FT=Fixed Termination) and a mobile part MT (PP=Portable Part with PT=Portable Termination) with the capability for telecommunications with the base station BS. This basic structure can be extended in accordance with the DECT Standard in such a manner that up to twelve such mobile parts MT are assigned to a single base station BS.
FIG. 3 shows such a cordless telephone system STS, in which a maximum of 12 links using the TDMA/FDMA/TDD method (Time Division Multiple Access/Frequency Division Multiple Access/Time Division Duplex) are set up on one DECT base station BS in parallel to DECT mobile parts MT1 . . . MT12 via a DECT radio interface designed for the frequency band between 1.88 and 1.90 GHz. The figure 12 results from a number xe2x80x9ckxe2x80x9d of time slots or telecommunications channels (k=12) available for duplex operation of a DECT system. The links may in this case be internal and/or external. In the case of an internal link, two mobile parts registered at the base station BS, for example the mobile part MT2 and the mobile part MT3, can communicate with one another. For setting up an external link, the base station BS is connected to a telecommunications network TKN, for example in wire-based form via a telecommunications access unit TAE or a private branch exchange NStA is connected to a wire-based telecommunications network or, in accordance with WO 95/05040, in wire-free form as a repeater station to a higher level telecommunications network. In the case of the external link, it is possible to communicate with a mobile part, for example with the mobile part MT1, via the base station BS and the telecommunications access unit TAE, and for a private branch exchange NStA to communicate with a subscriber in the telecommunications network TKN. If, as in the case of the Gigaset 951 (Siemens cordless telephone, cf. telecom report 16, (1993), issue 1, pages 26 and 27 BSxe2x80x94the base station) has only one connection to the telecommunications access unit TAE or the private branch exchange NStA, then only one external link can be set up. Ifxe2x80x94as in the case of the Gigaset 952 (Siemens cordless telephone, cf. telecom report 16, (1993), issue 1, pages 26 and 27)xe2x80x94the base station BS has two connections to the telecommunications network TKN, then, in addition to the external link to the mobile part MT1, a further external link is possible from a wire-based telecommunications terminal TKE connected to the base station BS. In this case, it is in principle also feasible for a second mobile part, for example the mobile part MT12, to use the second connection for an external link, instead of the telecommunications terminal TKE. While the mobile parts MT1 . . . MT12 are operated using a battery or a rechargeable battery, base station BS, which is designed as a small cordless switching system, is connected via a mains connecting unit NAG to a power network SPN.
The cordless telephone system according to FIG. 3 is preferably used in the private area, according to FIG. 2.
In the small public areaxe2x80x94in accordance with FIG. 2xe2x80x94a plurality of such cordless telephone systems according to FIG. 3 can be operated as a cellular system on a private branch exchange PABX (Private Automatic Branch Exchange), the private branch exchange PABX controlling a plurality of base stations A-BS, B-BS, C-BS and, if required, supporting a handover from one base station to another. FIG. 2 also shows six mobile parts MTa . . . MTf which are assigned to the three base stations A-BS, B-BS, C-BS. This results in a cellular cordless telephone system in which the telecommunications link as a rule passes via that base station A-BS, B-BS, C-BS with which the mobile part MTa . . . MTf has the best radio contact.
Based on the document xe2x80x9cNachrichtentechnik Elektronik [Electronic Information Technology]xe2x80x9d42 (1992) January/February, No. 1, Berlin, DE; U. Pilger: xe2x80x9cStruktur des DECT-Standards [Structure of the DECT Standard]xe2x80x9d, pages 23 to 29 in conjunction with the ETS 300 175-1 . . . 9, October 1992 FIG. 4 shows the TDMA structure of the DECT system STS. In terms of multiple access methods, the DECT system is a hybrid system in which radio messages can be transmitted on ten frequencies in the frequency band between 1.88 and 1.90 GHz using the FDMA principle and, according to FIG. 4, in a predetermined time sequence using the TDMA principle, from the base station BS to the mobile part MT and from the mobile part MT to the base station BS (duplex operation). The time sequence is in this case governed by a multiple time frame MZR, which occurs every 160 ms and which has 16 time frames ZR, each having a time duration of 10 ms. Information is transmitted separately in these time frames ZR to the base station BS and to the mobile part MT, this information relating to a C, M, N, P and Q channel defined in the DECT Standard. If information for a number of these channels is transmitted in one time frame ZR, then the transmission takes place based on a priority list where M greater than C greater than N and P greater than N. Each of the 16 time frames ZR in the multiple time frame MZR is in turn split into 24 time slots ZS each having a time duration of 417 xcexcs, of which 12 time slots ZS (time slots 0 . . . 11) are reserved for the transmission direction xe2x80x9cbase station BSxe2x86x92mobile part MTxe2x80x9d and a further 12 time slots ZS (time slots 12 . . . 23) are reserved for the transmission direction xe2x80x9cmobile part MTxe2x86x92base station BSxe2x80x9d. Information having a bit length of 480 bits is transmitted in each of these time slots ZS, in accordance with the DECT Standard. Of these 480 bits, 32 bits are transmitted as synchronization information in a SYNC field, and 388 bits as wanted information in a D field. The remaining 60 bits are transmitted as additional information in a Z field and as guard information in a xe2x80x9cGuard Timexe2x80x9d field. The 388 bits in the D field transmitted as wanted information are in turn split into a 64-bit long A field, and a 320-bit long B field and a 4-bit long xe2x80x9cX-CRCxe2x80x9d word. The 64-bit long A field is composed of an 8-bit long data header, a 40-bit long data set with data for the C, Q, M, N and P channels and a 16-bit long xe2x80x9cA-CRCxe2x80x9d word.
Based on the document Components 31 (1993), Issue 6, pages 215 to 218; S. Althammer, D. Brxc3xcckmann: xe2x80x9cHochoptimierte IC""s fxc3xcr DECT-Schnurlostelefone [Highly optimized ICs for DECT cordless telephones]xe2x80x9d, FIG. 5 shows the basic circuit layout of the base station BS and of the mobile part MT. According to this, the base station BS and the mobile part MT have a radio section FKT with an antenna ANT which is associated with transmission and reception of radio signals, a signal processing device SVE and a central controller ZST, these items being linked to one another in the manner illustrated. The radio section FKT essentially contains known devices such as the transmitter SE, receiver EM and synthesizer SYN as well as a field strength measuring device RSSI (Radio Signal Strength Indicator), which are linked with one another in a known manner. The signal processing device SVE contains, inter alia, an encoder/decoder device CODEC. The central controller ZST has a microprocessor xcexcP both for the base station BS and for the mobile part MT, with a program module PGM designed in accordance with the OSI/ISO layer model (cf. (1): Information leafletsxe2x80x94Deutsche Telekom year 48, February 1995, pages 102 to 11; (2): ETSI Publication ETS 300175-1 . . . 9, October 1992), a signal control section SST and a digital signal processor DSP, which are linked to one another in the manner illustrated. Of the layers defined in the layer model only the first four layers, which are absolutely essential for the base station BS and the mobile part MT are illustrated. The signal control section SST in the base station BS is designed as a Time Switch Controller TSC, and that in the mobile part MT is designed as a Burst Mode Controller BMC. The major difference between the two signal control sections TSC, BMC is that the base-station-specific signal control section TSC also carries out switching functions (switch functions) in comparison with the mobile-unit-specific signal control section BMC. The signal control sections TSC, BMC each contain a counting device ZE with a bit, time slot and time frame counter.
The basic method of operation of the circuit units mentioned above is described, for example, in the document cited above, Components 31 (1993), Issue 6, pages 215 to 218.
The described circuit layout according to FIG. 5 in the base station BS and the mobile part MT is supplemented by additional functional units in accordance with their function in the DECT system according to FIG. 3.
The base station BS is connected to the telecommunications network TKN via the signal processing device SVE and the telecommunications access unit TAE or the private branch exchange NStA. As an option, the base station BS may also have an operator interface (functional units shown by dashed lines in FIG. 5), which comprises, for example, an input device EE designed as a keypad, an indicating device AE designed as a display, and speech/listening device SHE designed as a handset with microphone MIF and an earpiece HK, as well as a ringer bell TRK.
The mobile part MT has the operator interface (which is possible as an option for the base station BS) with the control elements which are part of this operator interface and are described above.
Like the base station BS in the private area, the private branch exchange PABX according to FIG. 2 is connected to the wire-based public telephone network PSTN (Public Switched Telephone Network). In this way, anyone can become his own network operator by obtaining a cordless telecommunications system comprising the private branch exchange PABX and the cordless telephones A-BS, B-BS, C-BS, MTa . . . MTf connected to it.
In order to make it possible to dispense with network coordination in this case, according to the DECT Standard, the Dynamic Channel Allocation method (DCA method) is provided. If, for example, a DECT link is being set up, a search is carried out for that frequency and that time window having the least interference. The level (intensity) of the interference depends primarily on whether
(a) a conversation is already being carried out on another base station, or
(b) as a result of movement, a mobile part comes into visual contact with a base station that was previously screened.
Any increase in interference resulting from this can be countered using the TDMA transmission method on which the DECT cordless telephone system is based. According to the TDMA method, only one time slot is used for the actual transmission; the other eleven time slots can be used for measurements. In consequence, it is possible to determine an alternative frequency/time slot pair, to which the link can be switched. This is done in the course of adaptive channel allocation in accordance with the DECT Standard (cf. (1) Nachrichtentechnik Elektronik [Electronic Information Technology] 42 (January/February 1992), No. 1, Berlin; U. Pilger: xe2x80x9cStruktur des DECT-Standards [Structure of the DECT Standard]xe2x80x9d; page 28, paragraph 3.2.6) and (2) EP-0 576 079 A1) by means of a xe2x80x9cConnection Handoverxe2x80x9d (Intra-Cell Handover).
In addition to this xe2x80x9cIntra-Cell Handoverxe2x80x9d, the xe2x80x9cInter-Cell Handoverxe2x80x9d or the seamless handover may also be mentioned, which is likewise possible in the course of DECT-specific adaptive channel allocation.
In order now to address in particular the xe2x80x9cInter-Cell Handoverxe2x80x9d problem which occurs regularly in cellular wire-free telecommunications systems according to EP-0 577 322 A1, the mobile radio receiver (mobile part) provided for such cellular radio telecommunications systems, must be able to change the base station, subject to a cell change within the cellular radio system, at any time during an active telecommunications link to a (quasi-) stationary radio transmitter (base station) (setting up a telecommunications link to another base station) while, at the same time, passing on the already existing active telecommunications link without any interruption (seamlessly) to the other base station (seamless handover). In this context, EP-0 577 322 A1 discloses the xe2x80x9chandoverxe2x80x9d being controlled by base stations involved and/or by a central mobile switching center (Mobile Switching Center MSC) connected to the base stations and, alternatively, by the relevant mobile part itself.
According to the document Nachrichtentechnik Electronik xe2x80x9c[Electronic Information Technology] 42 (January/February 1992) No. 1, Berlin; U. Pilger: xe2x80x9cStruktur des DECT-Standards [Structure of the DECT Standard]xe2x80x9d; page 28, paragraph 3.2.6, the DECT Standard provides for this purpose that the mobile part autonomously sets up a second telecommunications link, in parallel with the existing link, in the event of any deterioration in the transmission quality of the existing telecommunications link, on the basis of indicators of the transmission quality (for example signal field strength, CRC values, etc.). In the case of this xe2x80x9cInter-Cell Handoverxe2x80x9d procedure, the fact that DECT mobile parts are continuously informed of the status of the channels available in the current environment in the course of the dynamic, decentralized channel allocation process (DCA method), is used in such a manner that the second link is set up on the basis of the entry in a channel list.
An interruption-free handover is possible using the above procedure only if the mobile part is located in a cellular radio system with synchronized base stations. In such a synchronous cellular radio system, the mobile part can then, in addition to the already existing telecommunications link to a base station (originating base station), set up at least one further link to another base station in another radio cell without losing the synchronism with the originating base station in the process. Such a synchronous cellular radio system can, however, be implemented only with considerable system complexity (cable or radio synchronization).
The object on which the invention is based is to provide mobile radio receivers for cellular radio telecommunications systems which allow interruption-free intercellular relaying (seamless xe2x80x9cintercell-Handoverxe2x80x9d) in particular even when (quasi-)stationary radio transmitters arranged in the cellular radio telecommunications system are not synchronized (asynchronous radio telecommunications system).
In general terms a mobile radio receiver for cellular radio telecommunications systems, which can communicate with a large number of (quasi-) stationary radio transmitters. The (quasi-) stationary radio transmitters are arranged in radio cells of the radio. telecommunications system for radio-cell-related transmission of radio messages which are included in a multiplex structure having a plurality of structure elements and allow telecommunications connections to be set up between the stationary radio transmitters and a mobile radio receiver. Each of the transmitters are connected to a telecommunications network, synchronously or asynchronously with respect to one another, via a switching center. A functional unit has the following means: first means for receiving and processing the radio messages; second means for producing and controlling the radio links to the (quasi-) stationary radio transmitters; and third means for detecting and evaluating additional information which indicates the radio link quality and is contained in the radio messages. A first radio link is produced and maintains a first (quasi-) stationary radio transmitter on the basis of receiving a first radio message which is included in first structure elements of the multiplex structure. This first radio link is used as a telecommunications link. The first to third means are designed and connected to one another such that in addition to the first radio link, at least one second radio link to at least one second (quasi-) stationary radio transmitter is produced and maintained in the background on the basis of receiving radio messages which are included in the second to n-th structure elements of the multiplex structure. The second radio link is intended to be used as a telecommunications link. Depending on the comparison between the link quality of the first radio link and the link quality of the second radio link, the respective link quality is determined from the evaluation of the respective radio-link-specific additional information. Either the first radio link continues to be used as the telecommunications link, or the second radio link is used as a new telecommunications link. The first to third means are designed such that the first radio link to the first (quasi-) stationary radio transmitter is controlled (bearer handover) by a cyclic reception change from the first radio message, which is included in the first structure element of the multiplex structure, to one of the radio messages which are included in the second to n-th structure elements of the multiplex structure.
In an alternative embodiment the second means have a number of counting devices corresponding to the number of radio links.
In another alternative embodiment the second means have a counting device and an offset store which is allocated to this counting device.
Advantageous developments of the present invention are as follows.
The first to third means are designed in such, a manner that the first radio link to the first (quasi-)stationary radio transmitter is controlled (Bearer Handover) by a cyclic reception change from the first radio message, which is included in the first structure element of the multiplex structure, to one of the radio messages which are included in the second to n-th structure elements of the multiplex structure.
The second means have a number of counting devices corresponding to the number of radio links.
The second means have a counting device and an offset store which is allocated to this counting device.
The counting devices each comprise a bit, time slot and a time frame counter.
The counting device is designed as a bit counter, and the offset store carries out the functions of a time slot and time frame counter.
The counting device and, possibly, the offset store are designed as software modules.
The counting device and, possibly, the offset store are designed as hardware modules.
The first to third means are designed and connected to one another such that the second radio link or links to the second (quasi-)stationary radio transmitter or transmitters is or are produced and maintained as a function of at least one predetermined additional-information-related threshold value being exceeded by an additional information value, which is obtained from the additional information received with the radio messages via the first radio link.
The first to third means are designed and connected, to one another in such a manner that the second radio link or links to the second (quasi-) stationary radio transmitter or transmitters is or are produced and maintained as a function of at least one predetermined additional-information-related threshold value being undershot by an additional information value, which is obtained from the additional information received with the radio messages via the first radio link.
The cellular radio telecommunications system is designed as a cellular cordless telecommunications system, the (quasi-)stationary radio transmitter is designed as a cordless base station, and the mobile radio receiver is designed as a cordless mobile part.
The cordless base station and the cordless mobile part are designed as cordless devices for transmitting radio messages in accordance with the DECT Standard.
The cellular radio telecommunications system is designed as a cellular mobile radio telecommunications system, the (quasi-) stationary radio transmitter is designed as a mobile radio base station, and the mobile radio receiver is designed as a mobile radio mobile part.
The mobile radio base station and the mobile radio mobile part are designed as mobile radio devices for transmitting radio messages in accordance with the GSM Standard.
The telecommunications network is designed as a public telephone network, ISDN network, private telecommunications network, mobile radio network or satellite radio network, and the switching center is designed as a private branch exchange.
The wanted information transmitted in the course of the telecommunications link represents spoken words, written words and/or images.
The multiplex structure is designed as an structure, and the structure elements contained in the multiplex structure are designed as time slots/channels.
By contrast with previously known mobile radio receivers, described initially, the mobile radio receiver which achieves the object according to the invention is able (at any time and as a result of the fact that, in particular, the first to third means can receive all the radio messages transmitted for possible radio links on frequencies, in time slots and/or in channels by a radio transmitter and allow radio links to be set up) to set up in the background (in addition to a first radio link used as a telecommunications link to a first (quasi-)stationary radio transmitter) at least one second radio link, which is intended to be used as a telecommunications link, to at least one second (quasi-)stationary radio transmitter, in particular within an asynchronous cellular radio telecommunications system. In this case, it is irrelevant for the proposed solution principle whether
(1) the cellular wire-free telecommunications system is a radio system in accordance with the DECT Standard or the GSM Standard,
(2) the radio messages which are transmitted from the stationary radio transmitters to the mobile radio receivers and allow radio links to be set up between the radio transmitter and the radio receiver are transmitted in accordance with the TDMA method, the CDMA method or a hybrid (for example FDMA/TDMA/CDMA method) access method.
In this case, it is advantageous if the mobile radio receiver carries out a DECT-specific xe2x80x9cBearer Handoverxe2x80x9d in order to prevent the masking (concealment), which occurs according to static viewpoints, of other radio messages by the radio link, which is used as a telecommunications link.
In addition, it is advantageous if the mobile radio transmitter/radio receiver has a number of counting devices intended to match the number of radio links and telecommunications links to be set up. In the normal case (handover case), two counting devices are provided in the mobile radio receiver (mobile part) according to FIGS. 7 and 8, these being required to set up telecommunications links to two (quasi-)stationary radio transmitters (base stations).
As an alternative to the solution, it is also possible to provide a single counting device in conjunction with an offset store, which is allocated to this counting device, in the mobile radio transmitter/radio receiver, for setting up the telecommunications links.
It is advantageous to set up the second telecommunications link at least after exceeding a threshold value defined with respect to reciprocal signal field strength values and/or CRC values or after undershooting at least one threshold value defined with respect to signal field strength values and/or reciprocal CRC values.